Sync and Video : Working with Video in Pro Tools : Video Tracks : Multiple Codecs on an Individual Video Track

Multiple Codecs on an Individual Video Track
(Pro Tools HD, Pro Tools with Complete Production Toolkit, and Pro Tools with an Avid Video Peripheral Only)
A single video track can contain video clips compressed with different video codecs of the same type of video. For example, you can add QuickTime files that were compressed using multiple codecs to the same video track.
However, once the first video file has been added to a session, all additional video files added to the Timeline must have the same video frame rate as the first video file.